To improve the drainage of a pneumatic tire, a tread pattern has been conventionally proposed in which a rotating direction of the tire is specified in one direction (arrow R). As shown in FIG. 2, in the tread pattern, peripheral main grooves 2 are provided in the center area of a tread surface 1, and numerous inclined main grooves 3, inclined diagonal-outward in a direction reverse to the specified rotating direction R of the tire, are provided from the peripheral main grooves 2 to shoulder areas at a predetermined pitch in a circumferential direction of the tire.
However, in this tread pattern, the shape of blocks B each sectioned by two adjacent inclined main grooves 3 and one peripheral main groove 2 is extremely narrowed at treading end portions Q. Accordingly, flexural rigidity is reduced in a width direction of the tire. As a result, there has been a problem that the driving stability is reduced on a dry road. As a measure for preventing this reduction in the driving stability, the blocks are enlarged. Nevertheless, the groove areas of the inclined main grooves are reduced by the amount of the enlargement, thereby causing reduction in the hydroplaning resistance.
Moreover, upon braking on a wet road, water flows from the inclined main grooves toward the peripheral main grooves. Hence, there has been a problem that the braking performance is reduced. As a measure for this reduction, the inclination directions of the inclined main grooves are reversed. However, water in the inclined main grooves flows into the peripheral main grooves upon advancing, and the drainage performance is reduced. This causes a problem that the hydroplaning resistance is reduced.